Field of Invention
The present invention relates to a linear regulator circuit, in particular a linear regulator circuit wherein a control terminal of a power switch can quickly respond to a variation in the input voltage by means of a body control unit coupled between the input voltage and a body of a transistor.
Description of Related Art
FIG. 1 shows a prior art linear regulator circuit 10 for converting an input voltage Vin to an output voltage Vo, wherein a power switch 11 is coupled between the input voltage Vin and the output voltage Vo, and an error amplifier 12 compares a feedback signal Vr which relates to the output voltage Vo (for example, the feedback signal Vr is generated from a divided voltage of the output voltage Vo) and a reference signal Vref, to generate an output controlling a control terminal 111 of the power switch 11, such that the power switch 11 operates to convert the input voltage Vin to the output voltage Vo.
Please refer to the waveforms of the input voltage Vin and the output voltage Vo shown at the right side of FIG. 1. When there is a noise (transient variation) in the input voltage, it can cause corresponding noises in the output voltage, to degrade the quality of the output voltage (poor power supply rejection ratio (PSRR)). For a better PSRR, U.S. Pat. No. 6,541,946 proposes a solution; however, the solution requires a large current source and a large capacitor, which increases the cost of the circuit and needs a larger circuit area.
In view of the demerit of the prior art, the present invention provides a linear regulator circuit for solving the above problem.